In processes involving the partial oxidation of hydrocarbons to produce synthesis gas, the gas stream from the partial oxidation reactor is often at temperatures of 1200.degree.-1500.degree. C. This hot gas stream is therefore a source of energy as well as process gas. In many instances, this energy is recovered by having the hot gas stream flow through tubes in a waste heat boiler wherein the heat is transferred to water and steam generated.
When the gas stream first enters the tubes in the boiler, it is very hot, and in view of its acceleration upon entering the tubes, very turbulent. This turbulence causes very high rates of heat transfer at the entrance to the tubes. This in turn can cause melting and, coupled with the corrosive materials in the gas stream, corrosion of the tubes is accelerated.
To alleviate this problem it has been proposed to use tubes having a flared entrance. However, these tubes usually are designed to have cooling water recirculated under pressure within the tube walls to cool the ends. The axial component of the hydraulic forces of the pressurized recirculating water in the flared tubes creates an axial loading that requires internal support in addition to that usually provided for the tubes. This support is particularly needed during start-up when the water side of the boiler is brought up to temperature and pressure before the oxidation reactor is fired to generate gas pressure. Without this additional internal support, the tubes can be overloaded and fail.